1. Field of the Invention
The present invention relates to prostheses. More particularly, the invention relates to ossicular prostheses, and specifically to total ossicular prostheses.
2. State of the Art
Hearing is facilitated by the tympanic membrane transforming sound in the form of acoustic sound waves within the outer ear into mechanical vibrations through the chain of ossicular bones (malleus, incus, stapes) in the middle ear. These vibrations are transmitted through the ossicular bones to the footplate of the stapes where micro or macro motion of this structure results in compression waves within the fluid of the inner ear. These compression waves lead to vibrations of the cilia (hair cells) located within the cochlear where they are translated into nerve impulses. The nerve impulses are sent to the brain via the cochlear nerve and are interpreted in the brain as sound.
Hearing efficiency can be lost to erosion of the ossicular bones. Various combinations or portions of the bones can be replaced. For example, the malleus and incus can be together replaced in a manner that leaves all or a portion of the stapes intact. Such a prosthesis is a partial ossicular replacement prosthesis, or PORP, and extends between the tympanic membrane and the stapes capitulum. A PORP provides relative stability as the prosthesis is stabilized on an intact portion of a remaining ossicle. Alternatively, the incus, malleus and stapes can all be completely replaced or bypassed by a total ossicular replacement prosthesis, or TORP, that extends from the tympanic membrane to the stapes footplate located over the oval window. Referring to Prior Art FIGS. 1 and 2, a TORP 10 as generally described in U.S. Pat. No. 6,618,625 is shown. The TORP 10 includes a head 12 for placement against the tympanic membrane and an adjustable length shaft 14 that extends from the head to the remnant footplate 16 of the stapes 18. The shaft 14 preferably includes alternating enlarged and reduced diameter portions 20a, 20b for adjustable engagement with a sleeve 22 in the head 12, and an enlarged base or foot 24 for increased support on the footplate 16. In addition, the head 12 may include a malleus arm 26 to provide some upper support for the prosthesis 10 relative to a remnant of a non-functional malleus. Nevertheless, the TORP 10 is inherently unstable as a result of the forces F1-F5 to which it is subject.
In order to overcome the instability of a different type of TORP, i.e., a fixed length prosthesis with a smooth shaft, it has been proposed that, when the stapes 18 remains intact, the shaft of the TORP be stabilized against the capitulum 28 (i.e., the upper cap of the stapes arching structure). See Vincent, R. et al., Ossiculoplasty with Intact Stapes and Absent Malleus: The Silastic Banding Technique, Otology & Neurotology, 26: 846-852 (2005). In the Vincent study, a silastic disk was cut and then a central hole was punched therethrough to define a circular band sized to fit snugly about the neck of the capitulum of an intact stapes. The band was placed about the capitulum and as the TORP is inserted into the middle ear for implantation, the band is stretched and the shaft of the TORP is introduced within the stretched opening. The TORP is moved into final implantation position, with its inferior surface resting on the center of the footplate, and the band is then released against the shaft against the stapes. There are significant challenges to positioning the band about the capitulum and TORP shaft in a manner that properly restrains the TORP to provide the desired stabilization, and which also prevents damage to the tendon of the stapedius muscle extending from adjacent the capitulum. In addition, it is difficult to expand the band to accommodate receiving the larger foot-end of the shaft during the implantation procedure.